In general, I am a believer in this - and it goes to the core of many of the two-sided business models expounded by my partners at Telco 2.0.
But... if the general notion of API exposure and consumption is truly believed by those at the network operators, shouldn't they be "eating their own dogfood"?
As a starting point, wouldn't you expect the amount of API value to be imported from other sources, to be roughly equivalent to the amount exported to these new customer groups?
Now obviously the operators' large databases and infrastructure probably gives them a natural bias here, but that's not to say that similar sources of convenience and value lie elsewhere, which could be bought in.
If APIs are genuinely *that* valuable & available in the short-term, telcos ought to be avid purchasers of each other's capabilities, or those from banks or Google or Facebook or numerous vertical-market specialists. If customer data is valuable, shouldn't a mobile operator want to get access to fixed customer insights, and vice versa?